Abrasive tool and process of manufacture

ABSTRACT

An abrasive tool having improved efficiency and cutting properties which is useful for dressing cutoff, grinding and other abrasive wheels is composed of a tough metallic matrix in which are embedded a number of uniformly dispersed diamonds each encircled by a substantially brittle cermet. The abrasive tool is prepared by coating the diamonds with a ceramic, establishing complete contact between a metal powder and the ceramic-coated diamonds and then hot pressing at a temperature above the sintering temperature of the metal.

United States Patent Inventor Oswald E. Olivieri Chatham, NJ.

Appl. No. 718,734

Filed Apr. 4, 1968 Patented Aug. 3, 1971 Assignee J. K. Smlt & Sons, Inc.

Murray Hill, NJ.

ABRASIVE TOOL AND PROCESS OF MANUFACTURE 12 Claims, 2 Drawing Figs.

US. Cl 125/11,

, 51/309,125/39 Int. Cl 1324b 53/12, C04b 3/16 Field ofSeareh 125/1 1,39;

[56] References Cited UNITED STATES PATENTS 2,401,087 5/1946 Lindquist 76/D1G. 12 2,147,843 2/1939 Jamar 76/D1G. 12 2,170,164 8/1939 Stone 76/D1G. 12 2,382,666 8/1945 Rohrig 76/D1G. 12 3,316,073 4/1967 Kelso 51/295 X Primary Examiner-Harold D. Whitehead Attorney-Kane, Dalsimer, Kane, Sullivan & Kurucz ABSTRACT: An abrasive tool having improved efficiency and cutting properties which is useful for dressing cutoff, grinding and other abrasive wheels is composed of a tough metallic matrix in which are embedded a number of unifonnly' dispersed diamonds each encircled by a substantially brittle cermet. The abrasive tool is prepared by coating the diamonds with a ceramic, establishing complete contact between a metal powder and the ceramic-coated diamonds and then hot pressing at a temperature above the sintering temperature of the metal.

ABRASIVE TOOL AND PROCESS OF MANUFACTURE BACKGROUND OF THE INVENTION This invention relates to a new abrasive tool and to a process for making the tool.

Abrasive tools with diamonds on the cutting face are old in the art. These and other abrasive tools however do not generally have a uniform distribution of diamonds throughout and consequently result in uneven wear and nonuniform distribution of cutting action over the tool surface. Recent proposals have been made in Kelso U.S.P. 3,3l6,073 for overcoming nonuniform distribution of diamond particles throughout the abrasive tool which involve a process of forming pellets with the diamond at the center surrounded by a sinterable metal bonding medium which forms the matrix of the abrasive tool. Although these abrasive tools have an improved distribution of diamonds, they are not entirely satisfactory in some applications because the sinterable bonding metal material immediately adjacent the diamond is tough and does not easily abrade away to expose the diamond and thus facilitate cutting and grinding. In this regard, a sinterable mixture of 50 percent tungsten carbide and 50 percent cobalt surrounding the diamond results in a tough matrix immediately adjacent the diamond and throughout the tool which absorbs impact but does not abrade way rapidly to expose alarge area of diamond for cutting and thus is less efficient as an abrading device. I I

Although many attempts were made to overcome the foregoing and other difficulties none, as far as I am aware, was entirely satisfactory when carried into practice commercially on an industrial scale.

BRIEF SUMMARY l have now discovered a new abrasive tool, arid a process for making this tool, which has a substantially uniform distribution of diamonds and an improved rate ofcutting and efficiency.

It is an object of this invention to provide an abrasive tool having improved efficiency in cutting and grinding.

Another object of this invention is to provide an economical process for making an abrasive tool having a substantially uniform distribution of diamonds throughout.

Other objects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 shows a perspective view of the abrasive tool brazed to a metal shank to form a dressing tool; and

FIG. 2 shows an enlarged view of the diamond encircled by a cermet and embedded in the metal matrix.

DESCRIPTION OF THE INVENTION Generally speaking, and in accordance with the present invention, an abrasive tool is provided which is adaptable for dressing cutofl", grinding and other abrasive 'wheels, and comprises a metal matrix in which are embedded a plurality of substantially uniformly dispersed diamonds each encircled by a substantially brittle cermet which facilitates uniform spacing and distribution of the diamonds in the metal matrix and improves cutting rate and efficiency of the abrasive tool. The cermet is composed almost entirely of a hard, abrasive ceramic, the interstices of which are substantially filled with small amounts of the matrix metal which bonds the diamond and ceramic and prevents the diamond from loosening even under extreme conditions of cutting and grinding.

Referring now to the drawings, FIG. 1 shows the abrasive tool 2 brazed to a steel body 3 to form a dressing tool 4 for an abrasive wheel. The abrasive tool is composed of a matrix metal 5 in which are embedded diamonds 6 encircled by a cermet 7 which facilitates spacing and uniform distribution of the diamonds throughout the abrasive tool.

FIG. 2 shows an enlarged view of one of the diamonds 6 encircled or surrounded by a cermet 7 with the cermet-encircled diamond embedded in ametal matrix 5.

The cermet is composed almost entirely of a hard, easily abradable ceramic material such, for example, as tungsten carbide, tantalum carbide, titanium carbide, chromium carbide, or mixtures thereof. The interstices of the ceramic are substantially filled with the matrix metal which serves to bond the particles of ceramic and the diamond and thus produce a strong tool. By the use of the term cermet, I mean a partial mixture of the ceramic and the matrix metal with no noticea ble chemical reaction between these materials and in which the metal is included in a substantial number of the interstices of the ceramic. The cermet is held together by a mechanical interlocking between the materials. Small amounts of the matrix metal, which, for example, can be cobalt, iron, nickel,

copper or mixtures or alloys thereof, substantially fill the interstices of the ceramic and the remainder forms the matrix.

The cermet serves to properly position the diamond and facilitates uniform distribution throughout the abrasive tool. In additiomthe cermet separates and acts as a spacer between the diamond and the matrix metal. It is also-believed that the cermet is primarily responsible for the improved rate of cutting and efficiency of the abrasive tool because it is extremely brittle and abrades rapidly to expose a larger area of the diamond and thus facilitate the rate of cutting and efficiency. The matrix, however, which consists essentially of a metal or alloy without appreciable amounts of other embrittling materials, e.g. tungsten carbide, is tough and can absorb impact without fracture resulting in a tool which combines the best features of a substantially brittle, readily abradable cermet and a tough, ductile matrix metal. When the diamond is sufficiently exposed, it will dress a grinding or cutoff wheel and minimize wear of the cermet and matrix. As the diamond wears down, the workpiece (i.e. the wheel being dressed) causes the substantially brittle cermet to abrade thus again exposing a fresh surface of the diamond with a resulting improvement in cutting rate and efficiency.

It is to be noted that the ceramic, e.g. tungsten carbide, of which the cermet is substantially composed, is nonsinterable at the sintering temperature of the matrix metal, e. g. cobalt.

This invention also contemplates a process of making an abrasive tool which comprises coating a mass of diamonds with a ceramic to form individual balls, dispersing a powdered metal around and in complete contact with the balls to form a mixture of ceramic-coated balls and metal powder; applying heat and pressure to the mixture in sufficient amounts to raise the temperature to at least the sintering temperature of the metal, maintaining the heat and pressure for a period sufficient to permit small amounts of the metal to fill the interstices of the ceramic and the remainder to form the matrix. The temperature and pressure are usually maintained for at least about 2 minutes to form the tool.

To give those skilled in the art a better understanding of the invention, the following illustrative example is given.

EXAMPLE A batch of diamonds, each approximately one two-hundredths of a carat in size, was placed in a coating bowl. The bowl was then rotated and tungsten carbide having a particle size between about 4 and 8 microns was sprinkled onto the rotating mass of diamondsalong with sugar and water to facilitate binding of the tungsten carbide particles to the diamond. The rotational motion of the bowl causes the tungsten carbide particles to adhere to the individual diamond particles and collect upon the surfaces of the diamonds to form balls. The tungsten carbide-coated diamonds were then removed from the coating bowl and screened. It was found that about 50 percent of the coated diamond balls were retained on a No. 5 diamant screen and the remaining 50 percent were retained on a No. 6 diamantscreen which indicated that about 50 percent had a diameter between about 0.047

inch and 0.057 inch and about 50 percent had a diameter greater than about-0.057 inch. The balls were then placed in a mold suitable for forming a rectangular-shaped abrasive tool and then 300 mesh cobalt metal power was dispersed throughout the mold, in contact with, and completely surrounding the balls. The mixture of balls and cobalt powder was then cold-pressed to permit a temporary shape to be formed suitable for hot pressing. The cold-formed abrasive tool was first placed in a graphite crucible and hot-pressed at about 2400 F. under a pressure of about 500 pounds p.s.i. for about 2 minutes, and thereafter cooled to room temperature. The resulting abrasive tool consisted of a cobalt matrix having a substantially uniform distribution of diamonds, each diamond encircled by tungsten carbide (the encircled diamonds on the exposed faces being easily visible to the naked eye) with small amounts of cobalt in the interstices of the tungsten carbide. The dressing tool was brazed to a steel shank similar to that shown in FIG. 1 of the attached drawing and then used to dress an abrasive wheel. The tool displayed an excellent rate of cutting and efficiency during the dressing operation.

To properly space the diamonds in the abrasive tool and to otherwise produce a tool having a substantially uniform distribution of diamonds, the cross-sectional area ratio of cermet to diamond on the cutting face of the tool is advantageously between about 3:1 and :1, depending upon the size of the diamond used. For example, a dressing tool having a total of about 2 carats of diamond advantageously has a cross-sectional area of cermet to diamond of about 4:1, while a dressing tool having a total of about 1 carat of diamond advantageously has a cross-sectional area of cermet to diamond of about 8:1.

Advantageously, the ratio of volumes of metal (including matrix metal and metal forming the cermet) to diamond is between about 7.911 and about 31.621. For example, an abrasive tool having a cobalt matrix and a tungsten carbide-cobalt cermet advantageously has, for a tool with 2 carats of diamond, a volume percentage of constituents of about l 1.2 percent diamond, about 50.7 percent tungsten carbide, and about 38.1 percent cobalt. A dressing tool having a total of about 1 carat of diamond has a respective volume of constituents of about 5.6 percent diamond, 53.9 percent tungsten carbide, and 40.5 percent cobalt. Numerous shapes of abrasive tools can be produced in accordance with this invention, including inserts for segmented saw blades, drilling and coring bits, inserts for grinding wheels and the like.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

What l claim is:

1. An abrasive tool, adaptable for dressing cutoff, grinding and other abrasive wheels, which comprises a tough metal matrix formed of pressed metal particles, the metal being selected from the group consisting of cobalt, iron, nickel and copper and alloys and mixtures thereof, in which matrix are embedded a plurality of substantially uniformly dispersed diamonds, each encircled by time particles of hard, abradable material, the hard carbide material being selected from the group consisting of carbides of metals such as tungsten, tantalum, titanium, chromium and mixtures, the particles of said hard carbide constituting an abradable barrier at the diamond surface in the matrix, theinterstices between the hard particles and the metal particles of the matrix being partly filled with small amounts of particles of the matrix metal due to pressing at high temperature for a short time, the bond between the diamond and the encircling material being readily abradable due to said hard material.

2. An abrasive tool in accordance with claim 1 wherein the hard material is tungsten carbide and the interstices are filled with particles of cobalt from the matrixmetah An abrasive tool in accordance with claim 1 wherein the hard material is tungsten carbide and the matrix is formed of particles of an iron alloy.

4. An abrasive tool in accordance with claim 1 wherein the cross-sectional area ratio of hard material to diamond on the face ofthe tool is between about 3:1 and 10:1.

5. A process of making an abrasive tool which is adaptable for dressing cutoff, grinding and other abrasive wheels, and which is composed of a metal matrix formed of pressed metal particles, the matrix having embedded therein a plurality of substantially uniformly dispersed diamonds each encircled by fine particles of hard abradable material, the interstices between the hard particles and the metal particles of the matrix being partly filled with small amounts of metal, said process comprising coating a mass of water-wet diamonds with fine particles of a hard carbide material to form individual balls, the particles of said hard carbide constituting an abradable barrier at the diamond surface in the matrix, dispersing a powdered metal around and in complete contact with the balls to form a uniform mixture of coated balls and metal powder, applying heat and pressure to the mixture in amounts sufficient to raise the temperature to at least the sintering temperature of the metal, and then maintaining the heat and pressure for a period sufficient to permit small amounts of the metal to fill the interstices between the matrix and the hard abradable particles surrounding each diamond to thereby form a shaped abrading tool.

6. A process in accordance with claim 5 wherein the hard abradable material is selected from the group consisting of tungsten carbide, tantalum carbide, titanium carbide, chromium carbide and mixtures thereof.

7. A process in accordance with claim 6 wherein the metal of the matrix is selected from the group consisting of cobalt, iron, nickel and copper and alloys and mixtures thereof.

8. A process in accordance with claim 5 wherein the mixture is heated to at least about 2400 F. and the pressure is maintained at least at about 500 pounds p.s.i. for at least about 2 minutes.

9. A process in accordance with claim 5 wherein the ratio of cross-sectional area of hard material to diamond on the face of the tool formed is between about 3:1 and 10:1.

10. A process in accordance with claim 5 wherein the mixture is first cold-pressed to the approximate shape of the tool before applying heat and pressure.

11. A process in accordance with claim 5 wherein the tool formed thereby is composed, by volume, of about 11.2 percent diamond, about 50.7 percent hard material, and about 38.1 percent metal.

12. A process in accordance with claim 5 wherein the tool formed thereby is composed, by volume, of about 5.6 percent diamond, about 53.9 percent hard material, and about 40.5 percent metal. 

1. An abrasive tool, adaptable for dressing cutoff, grinding and other abrasive wheels, which comprises a tough metal matrix formed of pressed metal particles, the metal being selected from the group consisting of cobalt, iron, nickel and copper and alloys and mixtures thereof, in which matrix are embedded a plurality of substantially uniformly dispersed diamonds, each encircled by fine particles of hard, abradable material, the hard carbide material being selected from the group consisting of carbides of metals such as tungsten, tantalum, titanium, chromium and mixtures, the particles of said hard carbide constituting an abradable barrier at the diamond surface in the matrix, the interstices between the hard particles and the metal particles of the matrix being partly filled with small amounts of particles of the matrix metal due to pressing at high temperature for a short time, the bond between the diamond and the encircling material being readily abradable due to said hard material.
 2. An abrasive tool in accordance with claim 1 wherein the hard material is tungsten carbide and the interstices are filled with particles of cobalt from the matrix metal.
 3. An abrasive tool in accordance with claim 1 wherein the hard material is tungsten carbide and the matrix is formed of particles of an iron alloy.
 4. An abrasive tool in accordance with claim 1 wherein the cross-sectional area ratio of hard material to diamond on the face of the tool is between about 3:1 and 10:1.
 5. A process of making an abrasive tool which is adaptable for dressing cutoff, grinding and other abrasive wheels, and which is composed of a metal matrix formed of pressed metal particles, the matrix having embedded therein a plurality of substantially uniformly dispersed diamonds each encircled by fine particles of hard abradable material, the interstices between the hard particles and the metal particles of the matrix being partly filled with small amounts of metal, said process comprising coating a mass of water-wet diamonds with fine particles of a hard carbide material to form individual balls, the particles of said hard carbide constituting an abradable barrier at the diamond surface in the matrix, dispersing a powdered metal around and in complete contact with the balls to form a uniform mixture of coated balls and metal powder, applying heat and pressure to the mixture in amounts sufficient to raise the temperature to at least the sintering temperature of the metal, and then maintaining the heat and pressure for a period sufficient to permit small amounts of the metal to fill the interstices between the matrix and the hard abradable particles surrounding each diamond to thereby form a shaped abrading tool.
 6. A process in accordance with claim 5 wherein the hard abradable material is selected from the group consisting of tungsten carbide, tantalum carbide, titanium carbide, chromium carbide and mixtures thereof.
 7. A process in accordance with claim 6 wherein the metal of the matrix is selected from the group consisting of cobalt, iron, nickel and copper and alloys and mixtures thereof.
 8. A process in accordance with claim 5 wherein the mixture is heated to at least about 2400* F. and the pressure is maintained at least at about 500 pounds p.s.i. for at least about 2 minutes.
 9. A process in accordance with claim 5 wherein the ratio of cross-sectional area of hard material to diamond on the face of the tool formed is between about 3:1 and 10:1.
 10. A process in accordance with claim 5 wherein the mixture is first cold-pressed to the approximate shape of the tool before applying heat and pressure.
 11. A process in accordance with claim 5 wherein the tool formed thereby is composed, by volume, of about 11.2 percent diamond, about 50.7 percent hard material, and about 38.1 percent metal.
 12. A process in accordance with claim 5 wherein the tool formed thereby is composed, by volume, of about 5.6 percent diamond, about 53.9 percent hard material, and about 40.5 percent metal. 